Device and method for the plastic forming of a workpiece made of metal or a metal alloy by means of ecap

ABSTRACT

A device for the plastic forming of a workpiece made of metal or a metal alloy by ECAP is described. The device comprises more than two channels, wherein an inlet channel and an outlet channel are provided, wherein these channels indirectly connect to one another and are arranged approximately perpendicularly to one another. Furthermore, a method for the plastic forming of a workpiece made of metal or a metal alloy ECAP is described. The workpiece is pressed once or multiple limes through a device having more than two channels, wherein the workpiece is plastically formed by a single or multiple pressing through an inlet channel and an outlet channel which indirectly connects to the inlet channel and is arranged approximately perpendicularly thereto.

The invention relates to a device for the plastic forming of a workpiecemade of metal or a metal alloy by means of ECAP, which device comprisesmore than two channels.

Furthermore, the invention relates to a method for the plastic formingof a workpiece made of metal or a metal alloy by means of ECAP, whereinthe workpiece is pressed once or multiple times through a device havingmore than two channels.

Devices for the plastic forming of a workpiece, made in particular of ametal alloy, by means of equal channel angular pressing (ECAP) are knownfrom the prior art. Known devices typically comprise two channels,wherein what is referred to as a forming bend is embodied between thechannels. Devices or methods of this type are generally suitable for theforming of a workpiece made of a metal alloy, such as a magnesium alloy,wherein good mechanical characteristic values are normally achieved.

Certain magnesium alloys are used, for example, to form bioresorbablestents or osteosynthesis components. A magnesium alloy must therebysatisfy multiple requirements to be able to be used as material formedical implants of this type. Aside from a high biocompatibility and alow decomposition rate, or a decomposition rate adapted to anapplication, an alloy of this type must also exhibit very goodmechanical properties, such as high strength, for example. Known ECAPdevices are suitable for the forming of a workpiece made of a magnesiumalloy for applications of this type, but even better mechanicalproperties are desired.

ECAP devices and methods for the plastic forming of a workpiece made ofa metal or a metal alloy are known, for example, from the articlePrinciples of equal-channel angular pressing as a processing tool forgrain refinement (R. Z. Valiev, T. O. Langedon, Progr. Mat. Sci. 51(2006) 881).

RU 2 181 314 C2 discloses a device for the plastic forming of aworkpiece made of metal. For the production of a workpiece having highstrength, the device comprises three channels, Wherein an inlet channeland an outlet channel are arranged parallel to one another. However,even with this device, it does not appear possible to produce aworkpiece with the desired mechanical properties.

The object of the invention is to specify a device of the type named atthe outset, with which device in particular a workpiece made of amagnesium alloy can be formed in an effective and efficient manner.

Another object is to specify a method of the type named at the outset,with which method a workpiece, made in particular of a magnesium alloy,can be formed with high strength being achieved.

The object is attained according to the invention in that, with a deviceof the type named at the outset, an inlet channel and an outlet channelare provided, wherein these channels indirectly connect to one anotherand are arranged approximately perpendicularly to one another.

An advantage obtained by the invention can in particular be seen in thata workpiece made of metal or a metal alloy, in particular a magnesiumalloy, can be produced with markedly improved mechanical properties bymeans of the device. For this purpose, it is provided that extendedlongitudinal axes of the inlet channel and of the outlet channelintersect approximately at a right angle. In particular, a workpiecehaving high strength can be produced, wherein the workpiece ispreferably pressed through the device multiple times. A forming of theworkpiece thus comprises a repeated pressing of the workpiece throughthe device. Compared to forming devices known from the prior art, aworkpiece having a higher strength can be produced with the deviceaccording to the invention, which workpiece can, after furtherprocessing, be used as a medical implant, for example. In particular, aquantity of the pressing operations through the device to produce apredefined strength is reduced. In addition, a maximum attainablestrength of the workpiece is also higher than with plastic forming usingan ECAP device known from the prior art.

It is advantageous if at least one additional channel is provided,wherein the inlet channel and the outlet channel are connected to oneanother by the at least one additional channel. The device is thusembodied for a double forming in each pressing operation. The workpieceis, for the forming of the same, preferably pressed through the devicemultiple times. Multiple channels can also be arranged between the inletchannel and the outlet channel. It is thereby always provided that theinlet channel is aligned approximately perpendicularly to the outletchannel.

It is advantageous if two channels are each arranged relative to oneanother such that they form a forming bend. Angles of consecutiveforming bends can be of an equal or different size. Thus, for example,an angle of a forming bend between the inlet channel and an additionalchannel connecting thereto can be approximately 75° to 135°, inparticular approximately 90° to 120°, particularly preferably 90°. Anangle of a forming bend between the additional channel and the outletchannel connecting thereto can be equal to the angle of the forming bendbetween the inlet channel and the additional channel connecting thereto,or can have an angle of a different size. This angle can, for example,be approximately 105° to 135°, in particular approximately 115° to 125°,particularly preferably 120°. it has been shown that such an embodimentof the device is particularly beneficial for producing a workpiece madeof a magnesium alloy with particularly high strength. Furthermore, aworkpiece having a very fine grain can be produced. If multiple channelsare arranged between the inlet channel and the outlet channel, an angleof a forming bend between two consecutive channels can in each case beof an equal or different size.

Expediently, a heating apparatus is provided. The heating apparatus isembodied for heating the device, and thus the workpiece, to apredetermined temperature, wherein the heating apparatus is arranged onthe device. In particular, with the heating apparatus it is possible tolower a temperature each time a workpiece, made in particular of amagnesium alloy, is pressed through the device. Thus, for example, thetemperature can be set to approximately 270° C. to 380° C., inparticular to approximately 300° C. to 350° C., for a firstpressing-through of the workpiece, whereas the temperature can be set toapproximately 190° C. to 270° C., in particular 220° C. to 240° C., fora last pressing-through. It can also be provided that the heatingapparatus lowers the temperature to room temperature by the lastpressing-through. Between a first and a last pressing of the workpiecethrough the device, the workpiece can be pressed through the device asoften as desired, wherein a temperature of the heating apparatus issteadily decreased. It generally holds that a device according to theinvention requires a lower temperature than known devices, whereby aworkpiece can be plastically formed in a more effective manner with thedevice according to the invention.

The other object is attained if, with a method of the type named at theoutset, the workpiece is plastically formed by being pressed once ormultiple times through an inlet channel and an outlet channel thatindirectly connects to the inlet channel and is arranged approximatelyperpendicularly thereto.

One advantage thus attained can in particular be seen in that aworkpiece having high strength is produced as a result. In addition, atendency of cracks to form in the workpiece is inhibited by the pressingthrough multiple channels. The workpiece is plastically formed by meansof ECAP, or equal channel angular pressing. One or more additionalchannels are arranged between the inlet channel and the outlet channel,wherein a forming bend is embodied between each two channels. As aresult, the workpiece is formed at least twice each time it is pressedthrough. The outlet channel is always arranged approximatelyperpendicularly to the inlet channel.

It is advantageous if, before each introduction into the inlet channel,the workpiece is rotated about a longitudinal axis of the same. Theworkpiece is thus formed into a workpiece that has a uniform strengthand is provided with a uniform fineness of grain. In addition, anattainable strength of the workpiece is increased.

It is beneficial if the workpiece is formed at least twice each time itis pressed through the device. For this purpose, the workpiece ispressed through at least three channels, wherein the inlet channel andthe outlet channel are always arranged perpendicularly to one another.In particular, the workpiece is pressed through three channels.

It is advantageous if the workpiece is pressed through multiplechannels, wherein a forming bend is provided between each two channels.The forming bends can have angles of an equal or different size. Forexample, two forming bends can be provided between three channels,wherein a first forming bend can have an angle of approximately 75° to135°, in particular approximately 90° to 120°, particularly preferablyapproximately 90°, and a second forming bend can have an angle of anequal size or, for example, an angle of approximately 105° to 135°, inparticular approximately 115° to 125°, particularly preferablyapproximately 120°. In a first forming of the workpiece, a tendency ofcracks to form in the workpiece is inhibited by the high hydrostaticpressure as a result of the forming bend, in particular of approximately90°. If multiple channels are arranged between the inlet channel and theoutlet channel, an angle of a forming bend between two consecutivechannels can in each case be of an equal or different size.

It is beneficial if the workpiece is heated, wherein a temperature islowered for each pressing of the workpiece through the device, in orderto efficiently form the workpiece. In particular, the workpiece isheated with a heating apparatus. Thus, for a first pressing-through of aworkpiece, made in particular of a magnesium alloy, a temperature is setto approximately 270° C. to 380° C., in particular to approximately 300°C. to 350° C., whereas the temperature is set to approximately 190° C.to 270° C., in particular 220° C. to 240° C., for a lastpressing-through. The temperature can also be lowered to roomtemperature by the last pressing-through. Between a first and a lastpressing of the workpiece through the device, the workpiece is pressedthrough the device as often as desired, wherein a temperature of theheating apparatus decreases in the direction of pressing.

Additional features, advantages and effects of the invention follow fromthe exemplary embodiment described below. In the drawings which arethereby referenced:

FIG. 1 shows a device according to the invention;

FIG. 2 shows experimental results of a tensile test;

FIG. 3 shows experimental results of a compression test;

FIG. 4 shows additional experimental results of a tensile test;

FIG. 5 shows additional experimental results of a compression test;

FIG. 6 shows experimental results of high strengths.

FIG. 1 shows a device 1 according to the invention for the plasticforming of a workpiece made of metal or a metal alloy by means of ECAP.The device 1 comprises an inlet channel 2 and an outlet channel 3,wherein the inlet channel 2 and the outlet channel 3 are connected by anadditional channel 4. The inlet channel 2 and the outlet channel 3, orthe longitudinal axes thereof, are arranged approximatelyperpendicularly to one another. Between the inlet channel 2 and theadditional channel 4, a forming bend with an angle a of approximately90° is provided, Furthermore, between the additional channel 4 and theoutlet channel 3, another forming bend is embodied, wherein this formingbend has an angle β of approximately 120°. The device 1 is thus embodiedas a double ECAP device.

In general, it can also be beneficial if multiple additional channels 4are provided between the inlet channel 2 and the outlet channel 3,wherein a forming bend is embodied between each two channels 2, 3, 4.

In FIGS. 2 and 3, experimental results of a tensile test and acompression test are shown. Data A for a workpiece in a startingcondition, data B for a workpiece formed using a known ECAP device, anddata C for a workpiece formed using the device 1 according to theinvention are thereby compared with one another. The workpiece is madeof a magnesium alloy and, for data B and data C, is in each case pressedmultiple times through a known device and a device 1 according to theinvention, respectively. Both the tensile test according to FIG. 2 andalso the compression test according to FIG. 3 show that the workpieceproduced using the device 1 according to the invention exhibits asignificantly higher strength. The workpiece is heated during both thepressing through the known device and also through the device 1according to the invention, wherein a temperature is lowered from 350°C. to 290° C. between a first pressing-through of the workpiece and alast pressing-through of the same.

Analogous data A, B and C are shown in FIGS. 4 and 5, wherein aworkpiece made of a magnesium alloy is once again formed and measured.However, the magnesium alloy differs in its composition from themagnesium alloy according to FIGS. 2 and 3. It is thereby also evidentthat the workpiece plastically formed using the device 1 according tothe invention exhibits a significantly higher strength than a workpieceproduced using an ECAP device having two channels. In this case, atemperature is lowered from 300° C. to 220° C., wherein the workpiece isonce again pressed multiple times through a known device and a device 1according to the invention. Data A once again originates from theuntreated workpiece.

FIG. 6 shows experimental results of a workpiece 1 made of a magnesiumalloy, which workpiece has been produced using a device 1 according tothe invention. Extremely high strength levels are achieved. A tensilestrength of the workpiece is approximately 468 MPa and an elastic limitof the same is approximately 413 MPa.

With the device 1 according to the invention and the method according tothe invention, a workpiece made of a metal or a metal alloy can beproduced in an efficient manner, which workpiece exhibits high strength,adequate ductility, high hardness, a uniform fineness of grain, and alow tendency to form cracks. A workpiece of this type is thereforesuitable, for example, for the production of a stent or other medicalimplants.

1. A device for the plastic forming of a workpiece made of metal or ametal alloy by means of ECAP, which device comprises more than twochannels, characterized in that an inlet channel and an outlet channelare provided, wherein these channels indirectly connect to one anotherand are arranged approximately perpendicularly to one another.
 2. Thedevice according to claim 1, characterized in that at least oneadditional channel is provided, wherein the inlet channel and the outletchannel are connected to one another by the at least one additionalchannel.
 3. The device according to claim 1, characterized in that eachtwo channels are arranged relative to one another such that they form aforming bend.
 4. The device according to claim 1, characterized in thata heating apparatus is provided.
 5. A method for the plastic forming ofa workpiece made of metal or a metal alloy by ECAP, wherein theworkpiece is pressed once or multiple times through a device having morethan two channels, in particular through a device according to claim 1,characterized in that the workpiece is plastically formed by a single ormultiple pressing through an inlet channel and an outlet channel whichindirectly connects to the inlet channel and is arranged approximatelyperpendicularly thereto.
 6. The method according to claim 5,characterized in that, before each introduction into the inlet channel,the workpiece is rotated about a longitudinal axis of the same.
 7. Themethod according to claim 5, characterized in that the workpiece isformed at least twice each time it is pressed through the device.
 8. Themethod according to claim 5, characterized in that the workpiece ispressed through multiple channels, wherein a forming bend is providedbetween each two channels.
 9. The method according to claim 5,characterized in that the workpiece is heated, wherein a temperature islowered each time the workpiece is pressed through the device.